This invention relates to a low solubility vegetable protein isolate and a process for producing the same.
Vegetable protein isolates, especially soy protein isolates have found a wide degree of utility as food ingredients. Typically, soy isolates are produced by processes which provide products with a relatively high nitrogen solubility index (NSI). Isolates with high NSI values generally have good dispersibility characteristics in aqueous systems and are preferred in food products where the protein isolate must also have a certain degree of functionality in the food product in addition to simply providing a source of protein. Functionality refers to the ability of the protein isolate to contribute to or interact with other ingredients of the food product in order to improve or maintain the desired chemical or physical characteristics in the food product. An example of this would be the addition of a protein isolate to an emulsified meat system wherein the protein isolate serves as a "binder" for the moisture and fat thereby improving the physical properties or texture of the meat system besides increasing or maintaining the desired level of protein.
By contrast, there are certain food product applications of protein isolates where a high degree of solubility is not desirable. An example of this is a non-aqueous, "creme" filling of the type normally found in cookies or snacks. These fillings usually comprise a mixture of a milk co-precipitate, shortening and sugar. The filling must be very spreadable, yet retain its softness for a prolonged period of time. The use of a highly soluble protein isolate or one having a relatively high NSI results in the formation of a very hard and brittle filling when used as a replacement for a portion of the milk protein. Why this is the case is not completely understood, however, if a low solubility isolate or one having a low NSI value is employed, the filling material is usually much better with desirable softness and spreadability. On the other hand, insolubility is not the sole criteria since if the protein becomes too insoluble, a "gritty" undesirable texture results in the filling. It would, therefore, be desirable if a protein isolate could be produced which has selective insolubility characteristics to provide a filling with the above properties.
It is, therefore, an object of the present invention to provide a low solubility protein isolate having the ability to function in a non-aqueous filling material.
It is also an object to provide a low solubility isolate having the physical ability to form a smooth, creamy, and spreadable filling.
It is an object to produce an isolate which will function in this fashion by a process that imparts selective insolubility characteristics to the isolate.
It is also an object to produce such an isolate by a process which is reliable and convenient to practice on a commercial basis.